Method of supporting phonograph reproducing systems



S ept. 24, 1929. c. P.- MADSEN 1729324 METHOD OF SUPPORTING PHONOGRAPH REPRODUCING SYSTEMS Filed Feb. 2, 1925 3 Sheets-Sheet l B M4 0. M

flTTORNEY P IN VEJV'TOR.

Sept. 24, 1929. c, P, MADSEN 1,729,224

METHOD OF SUPPORTING PHONOGRAPH REPRQDUCING SYSTEK S Filed Feb. 2, 1925 3 Sheets-Sheet 2 INVENTOR. M 6 MM Q/IZTTOli/NEY Sept. 24, 1929. C P MADSEN 1,729,224

METHOD OF SUPPORTING PHONOGRAPH REPRODUCING SYSTEMS I Filed Feb. 2, 1925 3 Sheets-Sheet 5 INVENTOR.

- Patented Sept. 24, 19 29 UNITED STATES PATENT orrlca cmLns r. MADSEII, or NEW YORK, N. Y., ASSIGNOR, BY mnsnn ASSIGNMENTS, 'ro WILLIAM w. vARNEY; or BALTIMORE, MARYLAND 4 METHOD OF SUPPORTING PHONOGRAPH BEPBODUGING SYSTEMS Application filed February bring the least side thrust of the reproducerneedle onttlie record consistent with keeping it engaged and malntaining said side thrust as near uniform as possible throughout the various convolutions of the record.

A further object of my invention is to position the plane of vibration of the reproducing means 0 radial respectively as the case may be, de-

' pending upon the type used as practicable,

-old cylinder machine, as,

maintaining substantially equal variations -at the extreme outer and inner convolutions trated in the accompanying drawings, wherein is shown the preferred embodiment of my invention .as applied to a phonograph, but it is understood that changes,.variations and modifications may be resorted to which come within the scope of the claims hereunto appended.

It is .well known thatthe re roducin system inany phonograph shou d not 0 y be able to iollow the groove or the cut of a record with the least possible resistance and also to allow for thevariations or mechanical im-. perfections in the record, but should approximate the same geometrical relation with every groove of the record duringfplaying. In the or instance, the Edison type,- it was customary to drive the reproducing system across the face of the cylinder with a solid collag actuated by a nut and threadiof the same pitch as the cut in the record. In this manner the relation of-the reproducer to the record remained quite eon-- stant and fixed at all points.

In the more modern disc recordmachines, however, such a device has been found to be a phonograph as near a tangent or.

2, 1925. Serial No. 6,41 5;

too clumsy and expensive, and it has been customary to support the reproducer at the end of a.'tube, called the tone arm, and swing'it from a pivoted point at some distance from the record, as illustrated in Figure 1, as shown in the diagrammatic drawing.

In this figure (Figure 1) .the line .AB represents a radius tothe center of the record and C a pivot point at some distance from the record, usually a distance at'least equalto the diameter of the record. The pivot is usually so placed that a line drawn from it ,to the radius AB will be at right angles to AB at a point about in the center of the musical grooves, that is, midway between the inner and outer circles of the record, The point E represents the position of'the needlepoint at the commencement of playing and the point- D at the end. It will be seen that the needle then 1s tangent to the record groove only when it 1s at'the point 0. At the commencement of playing at point E there is an appreciable angle formed with the tangent depending on the osition of the point C, and when at point D t e angle to the tangent is still greater, the degree of the' angle from tangency depending, of course, upon the position of point C. a

In the specific'case given, the distance from C to O is that of the diameter of the record, usually ten inches. Then the angle from tangency at E will be about 7 degrees and that at D about twelve degrees. This condition results in two' difiiculties: changes the timbre or tone quality 0 the reproduction as the playing progresses, and

pm, a,

second, it increases the wear on the record,

particularly toward the end-or inner circle.

I have dlscovered a relation which permits of swinging a reproducing system from a pivot at substantially the same distance from the center of the record as the diameter of the record and which'still maintains the diaphragmor needle rocker in substantial tan gency to every groove on the record.

Referring now to Figure 2: AB again i represents a radius from'the center through both concentric circles. CD represents a line at right angles to AB," commencing from the ice gent to the inner convolution since it is at right angles to the radius from the center. At the point of intersection of the radius with the outer convolution at E I also erect a right angle. line FE of the same length. This now also is tangent. I find that if I now support an L-shape tone arm or supporting lever at C, whose outer le .is e ual to CF and the other leg equal to E, with the reproducer at E, a substantially tangent position of the rocker needle will be maintained to every convolution. The rocker needle or diaphragm is tangent at the outer convolution by definition. If now as the point E moves across the record toward D, it also goes forward so that it is contacting on a different radius in every convolution until when it reaches G, if a line be drawn from A through it and a right angle to said line it will'be found to substantially coincide with a tangent to the convolution at point G. I

In actual construction'it isnot necessary to make the support arm in the form shown in this figure, but one may instead use that shown in Figure 3, in which case the pivot is still C on the same parallelogram. The lever, instead of proceeding from G to F is substantially the diagonal of the parallelogram, but the support means for theneedle is so arranged at the end that in the case of an ordinary re'producer the diaphragniis parallel with the ine EF.

Referring -t Fig. 3, with the tone arm pivoted at C and the diaphragm tangent-at the diaphragm is swung to the outer convolupoint E to the convolutions'at that point when swung .over to the pointGr, the diaphragm is about 5 degrees from being tangent to-the convolutions at that point. This can be overcome and a perfect tangent had at G, if desired, by fulcruming the arm (that is, move point C to G at C thus correcting the variation of 5 degrees above mentioned; but this will not produce a true tangent of the diaphragm to the outer convolution when swung over. If, however, we retain the fulcrum C and slightly lengthen the arm so that the diaphragm is tangent at G then when tion it will be. within 2 degrees of tangent to said convolution. In the specific case the lengthening of the line FE amounts to about inch. In practice this latter method works the-better. The outer circle is so much larger than the inner one that this slight lack of tangency has no appreciable effect as there will.

be 'a tendency then to steady the needle against one side of the groove. This method reduces the side thrust.

If the'parallelogram figure of Fig. 2 be viewed as a force diagram, it will be seen that there is a resultant of forces inward toward the center of the record, which is proportional to the length .of line CF, to line FE. It is foundby measurement that under ordinary conditions with a reproducer system having the usual weight of six ounces that. the forward pull or force along the line FE amounts to about one and two-tenth ounces when the laten is revolving clock-wise and the pull is ongitudinalfrom fulcrum C. It therefore follows that if the line FE is ten inches long and the line CF is two and a half inches long that the side thrust of the needle at F is about one-fourth .of one and two-tenth ounces, or slightly under one-fourth of an ounce. This slight side thrust is of an advantage because it insures the needle hugging continually one side of the record groove. The reason this is an advantage is that the steel needles commonly used do not perfectly fit the groove. There isconsequently a slight loss of motion when the groove swings the needle sideways. If, however this side thrust is too great, it will break downthe grooves of the record. I have found, however, that therelation given above produces a firmer reproduction and does not wear the record excessively.

If the first method of location is used, that is moving C to C in-Figure 3were used, the tendency is to increase the side thrust. If the point C is nearer to the line AB than the diameter of the record, this side thrust is also too greatly increased. Referring to thedrawings illustrating my invention, I have already discussed Figures 1, 2 and 3. Figured is a plan view of a phonograph, the supporting arm ofwhich'is.

positioned in accordance'with my improved system as,herein described; Fig. 5 .shows a fulcrum of which tone arm has been posi-- tioned in accordance with my improved sys term sothat the diaphragm is substantially tangent both to the inner and outer convolutions of the record; Fig.7 is a view in elevation, partly in section, of a phonograph shown in Fig. 6; Fig. 8 is a view of a fragmentary detail on an enlarged scale of the reprodu'cer shown in Fig. 4, looking in the direction of the arrow upon the face of the same. Y

Having thus described my invention, what I claim and desire cut is:

1. In an organized phonograph of the disc type a supporting arm for the .reproducer in use whereby the stylus of the reproducer op-' erates in a vertical plane tangent to the convolution of the'groove of the record, or within the limit of four degrees thereof at the inner convolution of the disc record in positionfor playing in said phonograph, and said st lus o erating'in a plane within-the limit ofyten egreesof the verticalplane tangent to secure by Letters Patto the outer convolution of the roove of said disc record, the fulcrum of sai supporting arm being a common center and relatively fixed for both positions.

2. In an organized phonograph of the disc type a supporting arm for the reproducer in use whereby the diaphragm of the reproducer operates in a vertical plane tangent to the convolution of the groove of the record, 0 or within the limit of four degrees thereof at the inner convolution of the disc record in position for playing in said phonograph, and said diaphragm operating in a plane within the limit of ten degrees of the vertical 0 plane tangent to the outer convolution of the groove of said disc record, the fulcrum of said supporting arm being a common center and relatively fixed for both positions. I

3. In an organized phono raph of the disc type a supporting arm for t e reproq cer in use whereby the stylus of the reproducer operates in a plane at right angles to the vertical plane tangent to the convolution of the groove of the record, or within the limit of four degrees thereof at the inner convolution of the disc record in position for playing in said phonograph, and said stylus operating in a plane Within the limit of ten degrees of the vertical plane at right'angles to the plane tangent to the outer convolution of the groove of said disc record, the' fulcrum of said supporting Tarm being a common center and relatively fixed for both positions.

4.,In an organizedphonograph of the disc type a su porting arm for the reproducer in use where y the diaphragm of the reproducer operates in a plane at right angles to the vertical plane tangent to the convolution of the groove of the record, or within the'limit of four degrees thereof at the inner convolution of the disc record in position for playing in said phonograph, and said diaphragm operating in a plane within the limit of ten degrees of the vertical plane at right angles to the plane tangent to the outer convolution of the groove of said disc .record, the fulcrum of said supporting arm being a common center and relatively fixed for both positions.

- CHARLES P. MADSEN. 

